1. Field of the Invention
The present invention relates to an image forming technique and, more particularly, to an image forming apparatus which advises the user of an adjustment execution timing in image formation and controls that adjustment execution timing.
2. Description of the Related Art
Conventionally, an electrophotographic image forming apparatus is known to suffer a change in image density due to, e.g., a change in photosensitive body or developing unit over a long period of time or a change in temperature or humidity of its ambient environment. To solve this problem, there is proposed a technique for adjusting a parameter factor, e.g., a charging bias or developing bias, which influences the density of a toner image, at an appropriate timing to stabilize the image density.
For example, to form a color image using a plurality of image carriers, such a technique detects predetermined pattern information (test patch) transferred onto a common transfer means such as a transfer belt which transfers visual images on the image carriers onto a transfer material. After that, it is a common practice to execute a method of controlling the toner density, a method of controlling the exposure amount, or a method of measuring the density of the test patch and correcting process conditions according to an image forming means.
To form a color image using a plurality of image carriers, there is also known a method of detecting a test patch and correcting timings to visualize images on the corresponding image carriers so as to correct color misregistration.
These image adjustment processes are periodically executed over a predetermined period of time when an image forming apparatus has satisfied a predetermined condition such as a preset cumulative print count. For example, if the current print count has reached a cumulative print count during execution of an image formation job, an image adjustment process is sometimes performed. In this case, for example, the current image density sometimes changes after the image adjustment process. Therefore, only periodical execution of an image adjustment process under a predetermined condition is insufficient to appropriately adjust degradation in quality of an image to be formed.
To solve this problem, Japanese Patent Application Laid-Open No. 10-307448 discloses an apparatus having an image adjustment function of allowing the user to execute an image adjustment process by manual operation if he/she determines that it is necessary.
Unfortunately, when the user is allowed to execute adjustment processes simply by manual operation in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 10-307448 described above, the following problems arise.
(1) Even immediately after the image forming apparatus has automatically executed an image adjustment process, the user cannot know time when the image adjustment process has been executed. In this case, the user may execute the image adjustment process by manual operation by mistake. This wastes consumables used for the image forming adjustment process and the time required for the image adjustment process.
(2) In particular, even when a print job including a small number of pages which may be printed with little concern for degradation in image quality is to be processed in a short period of time, an image adjustment process is uniformly, automatically executed on the basis of a predetermined condition. Since the image adjustment process is performed during execution of the print job, processing of the print job is interrupted. This greatly prolongs the processing time of the print job.
(3) Even when image adjustment has been executed by manual operation, if the image adjustment process is automatically executed on the basis of a predetermined condition, the current image quality changes after the image adjustment process in processing one print job as described above.
The present invention has been made in consideration of the above problems in the prior arts, and has as its object to provide an image forming technique for allowing the user to grasp a criterion until the next image adjustment process execution, so as to select an image adjustment process execution schedule in accordance with the degree of degradation in image or an image formation job to be processed.